1. Field of the Invention
The present invention relates to fiber optic networks. More particularly, the present invention relates to a system and method for integrating a fiber optic fixed access network and a fiber optic radio access network.
2. Background Information
Fiber optics have been used extensively in transport networks over the last ten to fifteen years and in fixed access networks over the last several years. With the foreseen and on-going deployment of fiber optics in fixed access networks, such as fiber-to-the-home (FTTH), fiber-to-the-building (FTTB), and fiber-to-the-curb (FTTC), a vast amount of fiber optics have been and will be installed in these fixed access networks. These fixed access networks will, in many cases, be Ethernet-based, providing best effort Ethernet services to customers.
Parallel to this deployment, development of future generation mobile networks with smaller and smaller cell radii will be installed. Cellular radio systems with digital fiber optic transmission between a radio unit (antenna part) and the base station will open up a new way of building and planning radio networks in the future. These future generation systems will hereinafter be referred to as fiber-to-the-antenna (FTTA). FTTA is a cost-effective way of distributing radio units in a cellular radio network with small to medium sized cells.
As shown in FIG. 1, a radio base station can comprise a main unit (MU) 150 and a radio unit (RU) 175. MU 150 and RU 175 may or may not be co-located. MU 150 includes the digital baseband components of a base station. For example, MU 150 can include a baseband component 105 and a digital intermediate frequency (IF) processing unit 110. Digital IF processing unit 110 digitally processes radio channel data at an intermediate frequency by performing such functions as filtering, channelizing, modulation, and so forth. RU 175 includes the analog radio parts of the base station. As used herein, a radio unit is the analog radio parts of a base station or other type of transceiver station with direct or indirect connection to a mobile switching center or corresponding device. A radio unit typically serves a particular cell in a cellular communication system. For example, RU 175 can include a receiver 130 connected to an antenna 135 for receiving radio communications from mobile subscriber units. Connected to receiver 130 is an analog-to-digital (A/D) converter 125. A/D converter 125 converts the analog radio communications received by receiver 130 into digital input for transmission to baseband component 105 via digital IF processing unit 110. RU 175 can also include a transmitter 120 connected to either the same or different antenna 135 for transmitting radio communications to mobile subscriber units. Connected to transmitter 120 is a digital-to-analog (D/A) converter 115. D/A converter 115 converts the digital communications received from baseband component 105 via digital IF processing unit 110 into analog output for transmission to the mobile subscriber units. In FTTA, communications traffic between MU 150 and RU 175 is transported over a fiber optic connection.
The primary problem with a fiber optic access network is the enormous cost of installing the fiber optic infrastructure itself, including trenching, opening-up streets, negotiating right-of-way, and so forth. Consequently, it would be advantageous to re-use an existing fiber optic infrastructure for more than one type of access network. FTTH- and FTTC-type networks will use, for example, Ethernet transmission for cost reasons. These networks will also provide fiber dense networks with many possible access points, which is beneficial for radio access network planning if these existing fiber optic networks could be used.
The FTTA link interface is generally not suitable to run using Plesiochronous Digital Hierarchy (PDH), Synchronous Digital Hierarchy (SDH), or Asynchronous Transfer Mode (ATM) transmission protocols. The FTTA link normally requires a synchronous, high-speed, point-to-point connection. Consequently, a separate fiber optic connection would be required for FTTA. Radio access networks and fiber-based fixed access networks are currently built as two separate networks, but installing a fiber optic network solely for FTTA is usually not cost effective.
Ethernet switches currently lack the performance necessary for radio applications. For example, the delays in buffers and inherent best effort properties of Ethernet switches have an impact on the performance of the radio communications traffic. The different synchronization and delay properties of radio communications traffic and Ethernet communications traffic will make it difficult to host both types of traffic in the same type of fiber optic network. For example, the timing requirements of the radio communications traffic are much more stringent than the best effort Ethernet communications traffic running on the Ethernet network. As a result, it is not possible to run time-sensitive radio communications traffic on a standard best-effort-type network. Since different packet sizes, prioritizations, and other delays will not be predictable, a method for secure and reliable transmission of low-delay radio communications traffic is necessary. In a network where the radio communications traffic might pass numerous switches and a complex access network with a high communications traffic load, the radio communications traffic cannot be transmitted with a guaranteed low delay.
It would be desirable to provide a system and method which allows a cellular (mobile) radio access network to coexist on the same fiber optic infrastructure as an Ethernet-based fixed access network.